Thermochemical Energy Storage for Renewable Grids: A Critical Review of Materials, Reactor Architectures, and Integration Strategies

Abstract

Thermochemical energy storage (TCES) has gained increasing attention as a practical pathway for achieving reliable, long-duration energy storage in systems dominated by intermittent renewable generation. Unlike conventional thermal storage, TCES relies on reversible redox and sorption reactions to store energy within chemical bonds, allowing for high energy density and negligible standing losses over extended periods. This review examines recent progress across the four principal components that shape TCES performance: thermochemical materials, reactor architectures, system-level integration, and modelling approaches. Current material candidates, including metal oxides, salt hydrates, and selected organic compounds, are evaluated in terms of reaction enthalpy, cycling stability, and techno-economic viability. Reactor concepts such as fixed-bed, fluidised-bed, and modular tubular designs are compared with respect to heat transfer characteristics, scalability, and suitability for applications ranging from concentrated solar power to industrial waste heat recovery and building-level thermal management. Key performance indicators, including gravimetric energy density, round-trip efficiency, and reaction kinetics, are reviewed alongside advances in thermodynamic, kinetic, and system-scale simulations. A distinguishing feature of this review is its integrated perspective, linking material-scale thermochemistry with reactor engineering and system-level operation to assess the practical scalability of TCES. The analysis highlights persistent barriers to deployment, particularly material degradation, limited heat and mass transfer, and the lack of standardised lifecycle assessment frameworks. Overall, while TCES presents a technically robust and versatile approach to grid-scale thermal storage, its widespread adoption will depend on coordinated advances in material development, reactor optimisation, intelligent control strategies, and pilot-scale validation across real operating environments.